1. Field of Invention
This invention is directed to methods and apparatuses for heating workpieces that are to be forged into metal parts. More particularly, this invention is directed to methods and apparatuses for heating workpieces (also known as billets, blanks or cuts) in such a way that different portions or "zones" of the workpieces are at different temperatures.
2. Description of Related Art
Many metal parts have distinct but integral portions that are of different configurations. An example is a part having a reduced portion at one end and an upset portion at the other end. Certain of these parts, including parts having reduced and upset end portions, must be manufactured, using present manufacturing processes and equipment, in separate and distinct steps-one step to form each distinct portion.
For example, it is known to form parts having a reduced portion at one end and an upset portion at the other end by first cold extruding a workpiece to form the reduced portion, and subsequently warm forging the workpiece to form the upset end. The reduced and upset end portions have not been formed by a single process, because (1) the upset end portion cannot be formed by cold extrusion and (2) both portions cannot be formed by a single warm forging stroke. As to the latter point, if a manufacturer attempted to manufacture such a part by a single warm forging stroke, the upset end of the workpiece would form first. Excessive tonnage (or compressive force) would then be exerted on the workpiece because the punch would be trying to force the already-upset workpiece into a reduced portion of the die cavity. This excessive force would result in underfilling of the reduced end portion (FIG. 6) of the part, while the upset end portion would have excess material or flash (FIG. 7).
It would obviously greatly increase productivity and reduce the cost of producing parts having distinct but integral portions of different configurations if the processing steps and/or equipment required to form the parts are reduced and/or simplified, e.g., if such parts can be produced in a single forging apparatus by a single forging stroke.
In this regard, parts having a flanged middle and concave recesses at the ends thereof have been produced in a single warm forging stroke by using a workpiece which has been heated such that its end portions have a temperature greater than the temperature of its center portion. However, certain parts having integral portions of other distinct and separate configurations cannot be formed by a single warm forging stroke using a workpiece which has been heated such that its end portions have a higher temperature than its middle portion, including parts having upset end portions and reduced end portions, as discussed above.
Accordingly, there is a need in the art for methods and apparatuses that enable manufacturers to form parts having integral portions of different configurations in a single process step using a single press.